Recombinant adenoviruses have emerged as attractive vehicles for in vivo gene transfer to a wide variety of cell types. The first generation vectors, which are rendered replication defective by deletion of sequences spanning E1, are capable of highly efficient in vivo gene transfer into nondividing target cells M. Kay et al, Proc. Natl. Acad. Sci. USA, 91:2353 (1994); S. Ishibashi et al, J. Clin. Invest., 92:883 (1993); B. Quinn et al, Proc. Natl. Acad. Sci. USA, 89:2581 (1992); M. Rosenfeld et al, Cell, 68:143 (1992); and R. Simon et al, Hum. Gene Thera., 4:771 (1993)!.
Immune responses of the recipient to the viral vector, the transgene carried by the vector, and the virus infected cells have emerged as recurring problems in the initial application of this technology to animals and humans. In virtually all models, expression of the transgene is transient and associated with the development of pathology at the site of gene transfer M. Kay et al, cited above; S. Ishibashi et al, cited above; B. Quinn et al, cited above; M. Rosenfeld et al, cited above; and R. Simon et al, cited above!. The transient nature of the effect of recombinant adenoviruses in most situations is the development of cellular immune responses to the virus-infected cells and their elimination. Antigenic targets for immune mediated clearance are viral proteins expressed from the recombinant viral genome and/or the product of the transgene. Studies in a variety of models suggest that first generation vectors express viral proteins in addition to the transgene which collectively activate cytotoxic T lymphocytes (CTL) leading to the destruction of the virus infected cells Y. Dai et al, Proc. Natl. Acad. Sci. USA, (in press); Y. Yang et al, Proc. Natl. Acad. Sci. USA, 91:4407 (1994); and Y. Yang et al, Immunity, 1:433 (1994)!. This problem is potentially overcome through the development of second generation recombinant viruses Y. Yang et al, Nat. Genet., 7:363 (1994); and J. Engelhardt et al, Hum. Gene Thera., 5:1217 (1994)!.
The other limitation of recombinant adenoviruses for gene therapy has been the difficulty in obtaining detectable gene transfer upon a second administration of virus. This limitation is particularly problematic in the treatment of chronic diseases, such as cystic fibrosis, that will require repeated therapies to obtain life-long genetic reconstitution. Diminished gene transfer following a second therapy has been demonstrated in a wide variety of animal models following intravenous or intratracheal delivery of virus T. Smith et al, Gene Thera., 5:397 (1993); S. Yei et al, Gene Thera., 1:192 (1994); K. Kozarsky et al, J. Biol. Chem., 269:13695 (1994)!. In each case, resistance to repeat gene therapy was associated with the development of neutralizing anti-adenovirus antibody.
There remains a need in the art for a method of improving the efficiency of gene transfer during repeated administrations of viral gene therapy.